1. Field of the Invention
The present invention generally relates to a pattern evaluation method, a pattern evaluation system, and a computer-readable recording medium.
2. Description of the Related Art
As an example of a conventional pattern evaluation method, a method for evaluating a fine pattern of a semiconductor will be described below.
Evaluation of a pattern is important in a semiconductor fabricating process. This is particularly conspicuous with respect to a fine pattern formed in a lithography process and/or an etching process. Conventionally, there is generally adopted a method for measuring and evaluating the dimension of a pattern (e.g., a line width in the case of a line pattern, a hole diameter in the case of a hole pattern) by means of a CDSEM (Critical Dimension Scanning Electron Microscope) using electron beams. In a CDSEM, a secondary electron profile is read from a pattern SEM image acquired from a sample, and an edge of a pattern is detected from the profile by an edge detecting algorithm. Then, the dimension of the pattern is calculated from coordinates of the detected edge by a CD measuring algorithm suitable for the purpose of each measurement. For example, when the line width of a line pattern intends to be obtained, right and left edges of the line are detected by the linear regression or threshold method from line pixels of an SEM image in electron beam scanning directions. With respect to the detected right and left edges, pairs of edges are obtained in a range specified by the measurement, and the average of the distances between the pairs of edges (the differences between X coordinates at edge points) is calculated as the line width of the line pattern. For example, in the case of a pattern which does not have a constant width, the maximum or minimum distance between the pairs of edges is calculated as the maximum width or the minimum line width, and the results thereof are outputted as a measured value.
However, in the above described conventional method, there is a problem in that it is not possible to carry out measurement unless the direction of a pattern to be measured (which will be hereinafter referred to as a CD direction) is coincident with the X-axis direction which is same as the scanning direction of electron beams in the case of an SEM. Therefore, for example, in order to eliminate such a problem, measurement is carried out after the scanning direction of electron beams is caused to be coincident with the CD direction, or measurement is carried out after an image processing, such as the affine transformation, is used for rotating an image to cause the CD direction to be coincident with the X-axis direction which is same as the scanning direction of electron beams in the case of an SEM. However, it takes an excessive time to carry out these processes, so that these processes are not preferably carried out in order to shorten the measuring time. Moreover, if the CD direction is not previously known prior to measurement, it is required to assign the scanning direction of electron beams in the case of an SEM or the image rotating angle to a certain range, so that it takes a longer time.
Similarly, if a hole pattern is an object to be measured, the maximum value of an SEM image in X-axis or Y-axis directions is measured as the hole diameter of the pattern in the conventional method. However, this method is difficult to obtain the maximum diameter, for example, if the maximum diameter of the pattern is inclined with respect to X-axis or Y-axis. In addition, in view of the distortion of the shape of the hole pattern, a method for calculating an approximate diameter from an area surrounded by edge points or a least square circle is carried out. However, it is impossible to grasp the shape of a complicated pattern only using these average measured values.